As is known, the formation of extruded foam products in the form of boards, planks and the like is enhanced by the employment of a vacuum chamber so that the expansion of the foaming material exiting an extrusion die takes place under sub-atmosphere pressure. To this end and because of the delicate and fragile nature of the extruded foam, foam extrusion lines have employed an inclined barometric leg of substantial length which, at its upper end, defines a vacuum chamber into which the foaming material is extruded and formed to its final shape before it is guided by a conveyor along the length of the barometric leg. At its lower end, the barometric leg extends at a shallow angle into a pool of water, and the conveyor continues through a large radius in the pool to guide the foam extrudate through and from the pool for further processing, such as cutting to size and length. In a full size extrusion line, the barometric leg may be more than 50 meters in length and the large radius portion of the conveyor in the pool may be more than 30 meters in length. Accordingly, the foam extrudate may have a length of more than 80 meters by the time the lead end thereof exits the pool.
Because the extruded product generally assumes a cross-section different than that of the die orifice through which it is extruded, extrusion dies advantageously have employed two spaced, adjustable die lips which together define therebetween an elongated, axially outwardly extending arcuate die orifice through which the foaming material moves both laterally and axially outwardly relative to the die lips. Since the die lips necessarily are located inside the vacuum chamber and thus inaccessible during extrusion, provision has been made for remotely adjusting the die lips from outside the vacuum chamber. The purpose of adjusting is to vary the size and shape of the die orifice which controls to a substantial degree the thickness and profile of the extruded product.
In order properly to adjust the extrusion die, thickness and profile measurements of the extruded foam must be made after the foam has taken its final shape. Heretofore, the measurements were taken after the foam product could be gotten to upon exiting the pool at the end of the barometric leg. As a result, a substantial length of off-specification or scrap product, such as more than 80 meters as indicated above, would have to be run before measurements were taken and the extrusion die adjusted accordingly. Moreover, the results of any adjustment would not be determined until an additional substantial length of product was run and measurements taken some five to twenty minutes later. Such procedure, needless to say, results in substantial scrap and lost time.